]]>By: Steve McIntyrehttp://climateaudit.org/2005/08/01/the-preisendorfer-on-centering-conventions/#comment-35250
Sun, 09 Oct 2005 17:45:45 +0000http://www.climateaudit.org/?p=287#comment-35250MBH98 doesn’t care whether a series goes up or down. It just changes the sign. PC series don’t actually have a sign – in group theory terms they are a “coset” but I don’t suppose that image will help anybody. The MBH99 PC1 points down, although the bristleonces point up. in the 2nd step, it gets regressed against a trend and signs get flipped.

A step function would have a different impact on the tree ring PC calculations and on the regression step. I’m offline now.

]]>By: fFreddyhttp://climateaudit.org/2005/08/01/the-preisendorfer-on-centering-conventions/#comment-35249
Sun, 09 Oct 2005 17:12:47 +0000http://www.climateaudit.org/?p=287#comment-35249Steve, isn’t it true that if the bristlecones had turned down in the 20th century, then that is the shape that the MBH procedure would have shown ( an upside-down hockey stick ) ?

And more generally, isn’t it right that the MBH procedure will mine for any series where the data points during the 20th century “training period” (or did they call it “validation period” ?) are markedly offset from the remainder of the data seres ? It seemed to me that you could replace the bristlecones with a step function with the diccontinuity in the year 1901, and that is what the end result would look like.

Or did I get hold of the wrong end of the (ahem) stick ?

]]>By: Mark Frankhttp://climateaudit.org/2005/08/01/the-preisendorfer-on-centering-conventions/#comment-35248
Sun, 09 Oct 2005 17:04:43 +0000http://www.climateaudit.org/?p=287#comment-35248Steve thanks and excuse me for making you go over ground you have clearly already covered.
]]>By: Steve McIntyrehttp://climateaudit.org/2005/08/01/the-preisendorfer-on-centering-conventions/#comment-35247
Sun, 09 Oct 2005 15:37:21 +0000http://www.climateaudit.org/?p=287#comment-35247Re: #22 and others: if you do a run with centered (covariance) PC calculations and retain 2 PCs (as in MBH98), you get high 15th century results (see MM05 (GRL)). If you do it without bristlecones, you get high 15th century results, regardless of the PC method. If you do centered PC and retain the PC4, you get low 15th century results. We survey various permutations and combinations in our E&E article as sensitivity comments not as saying that any method is a “right method”. Within “centered PC methods”, there are also covariance and correlation PC methods.

We have tried to maintain attention to both data and methodology issues. I don’t like the idea of a “beauty contest” (or an “ugliness contest”) to say which is the REAL problem. We don’t say that their results are “simply” an artifact of their PC method, since you can get low 15th century results with a centered PC method. A phrase that I like is: the flawed method interacts with the flawed proxies to create a “perfect storm”. We discovered the role of the bristlecones by actually following the flawed method to see what it did: it highlighted the bristlecones. I don’t think that a sensible answer can or should depend on how you apply Preisendorfer’s Rule N (and I’m not persuaded that it was ever used in the tree ring networks in the first place – I think that it’s been proposed ad hoc to try to salvage inclusion of the PC4).

In MM05 (EE), we characterized these results in terms of robustness rather than correctness – although this buance seems to have been totally lost in debate, largely because of realclimate disinformation. One of the warranties of MBH (and I like to use contractual terms like warranty) was that it was robust to the presence/absence of dendroclimatic indicators. (I’ve cited reliance of Bunn et al [2005] on exactly this claim.) But it’s results are obviously not robust to presence/absence of bristlecones.

]]>By: Mark Frankhttp://climateaudit.org/2005/08/01/the-preisendorfer-on-centering-conventions/#comment-35246
Sun, 09 Oct 2005 15:20:53 +0000http://www.climateaudit.org/?p=287#comment-35246#21 Dave – I think what you are saying is “yes” you still get a hockey stick shape with centred PCA and the real issue is the presence of the bristlecones.

So – simple question that has probably been answered a thousand times – but I can’t find it. What happens if you use centred PCA without the Bristlecones?

As far as I remember it’s the using a centered PCA that results in the hockey-stick moving from PC1 to PC4 (or is it PC5) and that’s what resulted in Preisendorfer’s rule entering into the picture. IOW most of the variance with a centered PCA get explained by other proxies, but it still takes the bristlecones to explain the hockeystick. This either means that the other proxies aren’t very good temperature measurers or that the instrumental record, with its pronounced hockeystick-blade shape, is flawed and takes a flawed proxy like bristlecones to reproduce it.

]]>By: Mark Frankhttp://climateaudit.org/2005/08/01/the-preisendorfer-on-centering-conventions/#comment-35244
Sun, 09 Oct 2005 11:04:38 +0000http://www.climateaudit.org/?p=287#comment-35244This thread appears to address a question I have being trying to answer the last few days.

Can Steve or someone confirm whether you still get a hockey stick shape using centred PCA? The dialogue above suggests you do. And if that is true, isn’t TCO right, that the real issue is the Bristlecone pine series? The use of non-centred PCA might exacerbate the problem but the hockey stick still exists without it.

Is there a diagram somewhere showing what the hockeystick looks like using centered PCA? Presumably it is different.